Methods and systems for controlling liquids in multiplex assays

ABSTRACT

A fluidic device for conveying liquid to a well of a microplate. The device includes a support structure configured to be mounted along the microplate. The device also includes a microfluidic tube coupled to the support structure. The tube has an inlet, an outlet, and an open-sided channel that extends longitudinally therebetween. The tube has a cross-section that includes an interior contour with a gap therein. The gap extends at least partially along a length of the tube. The tube is configured to convey liquid to the well of the microplate when the tube is held in a dispensing orientation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/143,027 (the '027 application), which was filed on Jun. 30, 2011 andis a national stage entry of International Application No.PCT/US2010/025071 (the '071 application), filed on Feb. 23, 2010, whichclaims the benefit of U.S. Provisional Application No. 61/160,174 (the'174 application), filed on Mar. 13, 2009. Each of the '027, the '071,and the '174 applications is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate generally to methods andsystems for biological and chemical analysis, and more specifically tofluidic methods and systems for preparing and using microarrays inbiological and chemical analysis.

Microarrays may be used in various types of biological and chemicalanalysis, such as in genomic research, drug screening, or screening forinfectious diseases. Microarrays generally include sample regions ofknown biomolecules, also referred to as probes, that are immobilizedonto a surface of a substrate, such as a slide. The probes may be, forexample, polynucleotides, proteins, other chemical compounds, ortissues. The sample regions are arranged on the surface (e.g., rows andcolumns) so that each sample region will have a known location oraddress on the surface of the substrate. The sample regions are thenexposed to a target solution containing biomolecules, also calledtargets, to determine if the targets bind to any of the probes.

For example, in one conventional system, the sample regions are locatedin an array at the bottom of a well in a microplate. A loading stationthat has several pipettes or syringes is used to deliver a drop of atarget solution into each of the wells so that the drop is placed ontothe corresponding sample region. The biomolecules of the target solutionare labeled so that the target biomolecules have an optically detectablequality (e.g, fluorescence). When exposed to the probes of the sampleregions, the target biomolecules selectively bind (e.g., throughhybridization) with certain probes. To facilitate the binding process,the microarray may be placed within an oven where the microarrayundergoes a predetermined thermal cycle. After the binding reaction iscompleted, the microarray is washed to remove any undesired residue andmay be then exposed to other solutions (e.g., another target solution,staining solutions). When ready, the microarray is scanned to determinewhich probes have a binding affinity for the target biomolecules. Forexample, if the target biomolecules were fluorescently labeled, a readercould scan the microarray to detect any fluorescence. The level offluorescence emitting from each sample region (or from particularportions of each sample region) indicates a binding affinity that theprobes and target biomolecules have for each other. The observedfluorescent pattern provides information on the sequence or structure ofthe target biomolecules.

However, the process for providing a solution to the sample regions mayhave certain limitations. For example, when the drop of the targetsolution is placed onto the corresponding sample region, small bubblesmay form within the drop on the surface of the substrate. If the bubblesare located on the sample region, the bubbles may prevent thebiomolecules of the target solution from interacting with the probes ofthe sample region. When the sample region is subsequently scanned, thoseportions of the sample region where the bubbles prevented theinteraction between the biomolecules and probes may not indicate thecorrect binding affinity. Some methods have been used for removing thebubbles from the target solution when the target solution has beendeposited onto the sample region. For example, each well of themicroplate may include a separate outlet or channel for removing gasesor bubbles formed within the solution. However, using a separate channelto remove the bubbles adds complexity to the system and may also reducethe available space on the microarray.

Another limitation is that conventional loading stations typically useautomated or robotic devices for delivering the target solution onto thesample regions. The loading stations are programmed to draw solutionfrom a source or reservoir (e.g., with pipettes or syringes) andautomatically deliver the solution to the wells of the microplate.However, the conventional loading stations are complex systems that maybe very expensive and require maintenance that is also costly.Furthermore, the loading stations may be limited in the types ofmicroarrays (e.g., size and density of sample regions) that arecompatible with the loading stations.

Accordingly, there is a need for improved systems, devices, and methodsfor reducing gases within a solution. There is also a need for improvedsystems, devices, and methods for conveying the target solution to thesample region in an efficient manner. Furthermore, there is a need forimproved methods and systems for fluidic control during biological orchemical assays.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one embodiment, a method for venting a well intowhich a liquid enters is provided. The method includes providing amicroplate having a well that includes a cavity with an open inlet and aclosed end. The cavity extends between the open inlet and the closedend. The cavity is defined by a wall surface having a cross-sectionalcontour that includes at least one continuous section and at least onediscontinuity section. The method also includes depositing a liquid intothe open inlet of the well. The liquid enters the cavity and flowstoward the closed end to at least partially fill the well. The liquidflows along the continuous section of the wall surface and remainsseparated from the discontinuity section of the wall surface, therebymaintaining a gas exhaust path along a spacing between the liquid andthe discontinuity section as the liquid flows toward the closed end topermit discharge of gas from the closed end of the well.

In a further embodiment, a microplate that is configured to facilitateventing a well that receives a liquid is provided. The microplateincludes a well having a cavity with an open inlet and a closed end. Thecavity extends between the open inlet and the closed end and is definedby a wall surface that has a cross-sectional contour. Thecross-sectional contour has at least one continuous section and at leastone discontinuity section. The liquid partially fills the well whendeposited therein. The cross-sectional contour is shaped to define aspacing between the discontinuity section and the liquid. The spacingproviding a gas exhaust path to permit discharge of gas from the closedend.

In yet another embodiment, a gasket that is configured to be mountedonto a substrate is provided. The gasket includes a body that isconfigured to be mounted to a surface of the substrate. The body has apair of sides separated by a thickness. The gasket also includes apassage that extends between the pair of sides through the body betweenan open inlet and an open outlet. The passage is defined by a wallsurface that has a cross-sectional contour that includes at least onecontinuous section and at least one discontinuity section. The passageforms a well with the surface of the substrate when the body is mountedthereon. The liquid partially fills the well when deposited therein. Thecross-sectional contour is shaped to define a spacing between thediscontinuity section and the liquid. The spacing provides a gas exhaustpath to permit discharge of gas from the well that the liquid enters.

In a further embodiment, a fluidic device for conveying liquid to a wellof a microplate is provided. The device includes a support structurethat is configured to be mounted along the microplate and a microfluidictube that is coupled to the support structure. The tube has an inlet, anoutlet, and an open-sided channel that extends longitudinallytherebetween. The tube has a cross-section that includes an interiorcontour with a gap therein. The gap extends at least partially along alength of the tube. The tube is configured to convey liquid to the wellof the microplate when the tube is held in a dispensing orientation.

In yet another embodiment, a method of conveying liquid from a sourcewell of a microplate is provided. The method includes inserting amicrofluidic tube into the source well of the microplate. The tube hasan inlet, an outlet, and an open-sided channel that extendslongitudinally therebetween. The tube has a cross-section that includesan interior contour with a gap therein. The gap extends at leastpartially along a length of the tube. The method also includes orientingthe tube with respect to a gravitational force direction into adispensing orientation and loading the liquid from the source well intothe tube. The liquid is exposed along the open-sided channel as theliquid flows down the tube.

In a further embodiment, a fluidic system configured to convey liquidbetween wells is provided. The system includes a first microplate thathas a source well and a second microplate that has a reaction well. Thesystem also includes a support structure that is configured to bemounted along at least one of the first and second microplates. Also,the system includes a microfluidic tube that is coupled to the supportstructure. The tube has an inlet, an outlet, and an open-sided channelthat extends longitudinally therebetween. The tube has a cross-sectionthat includes an interior contour with a gap therein. The gap extends atleast partially along a length of the tube. The tube is configured toconvey liquid to the well of the microplate when the tube is held in adispensing orientation. The outlet of the tube is held in the reactionwell of the second microplate and the inlet of the tube is inserted intothe source well of the first microplate to convey liquid from the sourcewell to the reaction well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a series of drops of liquid on different surfaces.

FIG. 2 is an exploded side view of a fluidic system formed in accordancewith one embodiment.

FIG. 3 is a perspective view of a fluidic device in accordance with oneembodiment that may be used with the fluidic system shown in FIG. 2.

FIG. 4 is a perspective view of a microfluidic tube that may be usedwith the fluidic device shown in FIG. 3.

FIG. 5 illustrates a pair of cross-sections C₁ and C₂ of the tube shownin FIG. 3.

FIGS. 6A-C illustrate different pairs of cross-sections corresponding tomicrofluidic tubes formed in accordance with alternative embodiments.

FIG. 7 illustrates the flow of liquid from a source well and into achannel of the tube shown in FIG. 3.

FIG. 8 is a side view of the flow of liquid from the channel of the tubeshown in FIG. 3 and into a reaction well.

FIG. 9 is an exploded view of a microplate formed in accordance with oneembodiment.

FIG. 10 is a top-plan view of a portion of the microplate shown in FIG.9.

FIG. 11 is a cross-sectional view of a reaction well taken along a line11-11 in FIG. 10.

FIGS. 12A-F illustrate cross-sectional contours of wells that may beused with a microplate formed in accordance with alternativeembodiments.

FIG. 13 is a flowchart of a method in accordance with one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein include various methods, devices, andsystems that use forces experienced by a liquid within a fluidic systemto control flow of the liquid and/or to vent or discharge gases from achamber into which the liquid enters. For example, in order to controlthe flow of the liquid and to deposit the liquid on a desired location,various embodiments may use gravitational force, cohesive forces, and/oradhesive forces to control the flow of liquid from a source or reservoirto a sample region. Various embodiments may also use gravitationalforce, cohesive forces, capillary forces, surface tension and/oradhesive forces to contain a liquid within a confined space and ventgases from the confined space.

In some embodiments, the flow and/or venting of the space where theliquid is located is facilitated by or is solely accomplished by passivemethods. As used herein, controlling the flow of liquid or the ventingof gases “passively” means utilizing energy that is innate to the systemor potential energy of the system to effect flow or venting.Accordingly, passive control of liquid flow or venting need not utilizekinetic energy produced outside of the system, for example, beingcarried out without using a pumping system to transfer the liquidbetween locations and/or to remove gases from the location. For example,some embodiments may transfer liquid from one location to another andvent gases without using syringes or pipettes to hold and relocate theliquid or separate channels to remove the gases. However, the pumpingsystems may, in some embodiments, include mechanical pumps or micropumpsand electroosmotic pumps. As another example of a passive method, theflow of liquid from a source well may be initiated by positivedisplacement, but the flow is maintained and controlled bygravitational, cohesive, and/or adhesive forces. However, otherembodiments are not limited to passive means, and the methods, devices,and systems described herein may be used in conjunction with pumpingsystems that actively control the flow of liquid and/or gases.

As used herein, a “sample region” includes any portion of a surface ofthe substrate where analytes of interest, such as biomolecules, arelocated. The sample region may also be referred to as a feature. Thebiomolecules may be immobilized onto the surface of the substrate in thesample region. In some embodiments, each sample region has a pluralityof smaller sample regions, or sub-features, that may also be arrangedinto an array (or sub-array) on the surface of the substrate. As usedherein, “biomolecules,” may be naturally occurring or synthetically madeand include polynucleotides, oligonucleotides, proteins, enzymes,polypeptides, antibodies, antigens, ligands, receptors, polysaccharide,carbohydrate, or any other chemical compound desired to be studied oranalyzed. Other analytes that are useful include small molecules,whether naturally occurring or synthetic and whether biologically activeor inert. Cells, tissues, organisms and the like are also usefulanalytes. The analytes may also be referred to as “targets” or “probes.”The biomolecules within a single sample region may be different or,alternatively, each sample region may include biomolecules having acommon chemical structure. Although several embodiments are exemplifiedherein with respect to biomolecules, it will be understood that otheranalytes can be used similarly.

As used herein, a “substrate” includes any structure that may hold thedeposited amount of liquid. For example, the substrate may be amulti-well plate or a slide with a planar surface. The substrate mayinclude an array of sample regions or may include only one sample regionthat, for example, covers most of or the entire surface of thesubstrate. In addition, the sample regions may be arranged in apredetermined manner such that each sample region is addressable (i.e.,the biomolecules in the sample region may be identified based upon thelocation of the sample region on the surface). Each sub-array within thecorresponding sample region may also be addressable. Furthermore, thesubstrate may have a planar surface or may include cavities, wells,grooves, and the like.

As used herein, a “microarray” generally includes a substrate that has aplurality of sample regions thereon for multiplex analysis. A microarraymay be a microplate having a plurality of wells (e.g., 96) where thesample regions are located. Also, a microarray may be a chip having aplurality of sample regions thereon where each chip is positioned withina well of a microplate or a larger microarray. As such, each well mayhave a microarray held therein.

A microarray used in a method described herein can have a plurality offeatures including, for example, at least about 100, 500, 1×10³, 5×10³,1×10⁴, 1×10⁵, 1×10⁶ or more features. The density of features on anarray can be, at least about 100, 500, 1×10³, 5×10³, 1×10⁴, 1×10⁵, 1×10⁶or more features per square centimeter. In particular embodiments, abead-based array can be used in which microspheres or beads are arrayedor otherwise spatially distinguished. Exemplary bead-based arrays thatcan be used in the invention include, without limitation, those in whichbeads are associated with a solid support such as those described inU.S. Pat. No. 6,355,431 B1; US 2002/0102578; and WO 00/63437, each ofwhich is incorporated herein by reference. Beads can be located atdiscrete locations, such as wells, on a solid-phase support, wherebyeach location accommodates a single bead. Alternatively, discretelocations where beads reside can each include a plurality of beads asdescribed, for example, in US 2004/0263923, US 2004/0233485, US2004/0132205, or US 2004/0125424, each of which is incorporated hereinby reference. The beads can be encoded by any of a variety of propertiesknown in the art including, without limitation, nucleic acid sequences,color, diffraction grating patterns and the like.

Any of a variety of arrays known in the art can be used in the presentinvention. For example, arrays that are useful in the invention can benon-bead-based. Particularly useful arrays are Affymetrix™ GeneChip®arrays, examples of which are described, for example, in U.S. Pat. No.7,087,732 or U.S. Pat. No. 6,747,143, each of which is incorporatedherein by reference. A spotted array can also be used in a method of theinvention. An exemplary spotted array is a CodeLink™ Array previouslyavailable from Amersham Biosciences. Another array that is useful in theinvention is one manufactured using inkjet printing methods such asSurePrint™ Technology available from Agilent Technologies. Arrays usedin various sequencing platforms are also useful such as those used forSolexa (now Illumina, Inc., San Diego, USA) sequencing technology asdescribed, for example, in US 2007/0015200; US 2004/0106110; US2003/0064398 or US 2003/0022207; those used in 454 Biosciences (nowRoche Diagnostics, Basel, Switzerland)) sequencing technology such asthose described in US 2006/0040297 or U.S. Pat. No. 7,211,390; or thoseused in Applied Biosystems (now Life Technologies, San Diego, USA)sequencing methods such as those described in US 2006/0024681 each ofwhich is incorporated herein by reference.

A “liquid,” as used herein, is a substance that is relativelyincompressible and has a capacity to flow and to conform to a shape of acontainer or a channel that holds the substance. The liquid may beaqueous based and include polar molecules exhibiting surface tensionthat holds the liquid together. The liquid may also comprise non-polarmolecules, such as in an oil-based or non-aqueous substance. A“microfluidic tube” includes a channel having dimensions in which thesurface tension and cohesive forces of the liquid and the adhesiveforces between the liquid and the surfaces of the channel have asignificant effect on the flow of the liquid. For example, a channel ofthe microfluidic tube may have a diameter that is less than 1 mm or,more specifically, less than 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1mm or 0.05 mm or less. Alternatively or additionally, the tube can havea maximum diameter of at most 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm,0.6 mm or 1 mm or more. As set forth elsewhere herein, the tube need nothave a circular cross section. Nevertheless, the cross section of thetubes can have an area that is equivalent to the area of the circularcross sections set forth above. Also, a path taken by the liquid alongthe microfluidic channel may be substantially linear or redirected inmany directions. The liquid may be deposited directly onto a desiredlocation from the microfluidic channel or the liquid may be depositedelsewhere on the surface and moved to the desired location. For example,a drop of liquid may be deposited onto a wall surface within a well andgravity may pull the drop along the wall surface and onto a bottomsurface within the well.

In some embodiments, an approximate or precise amount of the liquid(e.g., a drop or an aliquot) may be placed onto the surface of thesubstrate covering the sample region. The drop may be partiallycontained, for example, within a well that has a limited volume or thedrop may rest upon a surface without being compressed or shaped bywalls. The liquid may form a bead on the surface or the liquid mayspread along the surface through wetting and/or by being compressed intothe surface.

FIG. 1 illustrates a series of drops of liquid L on different surfaces.As discussed above, embodiments described herein utilize the forcesexperienced by the liquid L to control the flow of the liquid L andventing of gas. These forces include cohesive forces (i.e., attractiveforces between like molecules of the liquid L) and adhesive forces(i.e., attractive forces between molecules of the liquid L and a solidsurface or vapor that surrounds the liquid). Cohesive and adhesiveforces arise from the interaction of atoms and molecules that arelocated along, for example, a liquid-vapor interface and a liquid-solidinterface. Another force that affects the flow of liquid in embodimentsdescribe herein is gravity or the gravitational force F_(g).

Depending upon the nature of the liquid L and the solid surface, FIG. 1shows various resting diameters D_(R1)-D_(R6) and contact angles θ₁-θ₆.A resting diameter D_(R) is the diameter of the drop of liquid Lon acorresponding planar solid surface where the drop of the liquid L is notcompressed or contained by walls. The resting diameter D_(R) is measuredparallel to the planar solid surface. A contact angle θ is the angleformed by the intersection of two planes (P₁ and P₂) tangent to theliquid L and the corresponding solid surface. When the contact angle θis greater than 90% the resting diameter D_(R) remains substantially thesame (e.g., D_(R5) and D_(R6) are about equal). The contact angle θindicates a wetting ability of the liquid to the surface. Wetting is aliquid's ability to spread along a solid surface. The wetting of a solidsurface by a liquid is controlled by the intermolecular interactions ofmolecules along an interface between the two phases. if the adhesiveforces are relatively greater than the cohesive forces, the wetting ofthe liquid to the surface is greater (i.e., the contact angle θ will besmall as shown with contact angles θ₁ and θ₂ in FIG. 1). If the cohesiveforces are relatively greater than the adhesive forces, the wetting ofthe liquid to the surface is smaller (i.e., the contact angle θ will belarge as shown with contact angles θ₅ and θ₆).

Surface tension in a liquid is caused by the cohesive forces of theliquid and, as such, can have an affect on the contact angle θ. As thesurface tension increases, an ability of the liquid to reduce itssurface area (i.e., bead up) also increases. Surfaces of solids,however, may be characterized as having a surface energy. As the surfaceenergy of a solid increases, the ability of the solid to interact withthe liquid also increases (i.e., the contact angle θ decreases). As anexample, when a liquid of low surface tension is placed on a solid ofhigh surface energy, the liquid spreads across the surface and has asmall contact angle θ. If a liquid has a high surface tension and isplaced on a surface of low surface energy, the liquid may form a bead onthe surface and have a high contact angle θ. As will be discussed ingreater detail below, the flow of the liquid L and the venting of gasesmay be determined by the surface tension of the liquid and the surfaceenergy of the solid surface.

In embodiments utilizing aqueous or polar liquids, the interactionbetween the liquid L and the solid surface can be characterized ashydrophobic or hydrophilic. As used herein, a solid surface ishydrophobic if it repels an aqueous or polar liquid. For example, thecontact angle θ between the aqueous or polar liquid L and thehydrophobic surface of the solid is typically greater than 90 degrees. Asurface is hydrophilic if it is attracted to an aqueous or polar liquidL. For example, the contact angle θ between the aqueous or polar liquidL and the hydrophilic surface of the solid will typically be less than90 degrees.

In other embodiments, a non-polar liquid, such as alkanes, oils, andfats may be used as the liquid L. Non-polar liquids may be attracted toa surface that has a hydrophobic interaction with aqueous or polarliquids. Likewise, non-polar liquids are not attracted to a surface thathas a hydrophilic interaction with aqueous or polar liquids. As such,hydrophobic and hydrophilic surfaces may be used with embodimentsdescribed herein to control the flow of a non-polar liquid and to ventchambers having the non-polar liquid therein.

Embodiments described herein utilize the contact angle or the wetting ofa liquid and a shape of a solid surface to control the flow of theliquid L and to vent gases from a confined space that the liquid Lenters. Other factors may affect the contact angle θ or the wetting of aliquid to a solid. For example, a purity of the liquid L or whether asurfactant is used may affect the surface tension of the liquid and themolecular interactions along the solid-liquid interface. A purity of thesolid or whether a coating is placed on the solid surface may affect thesurface energy of a solid. Also, temperature of the environment, acomposition of the surrounding air, and the roughness or smoothness ofthe surface may all affect the interactions between the liquid L and thesolid surface.

The concepts discussed briefly above are discussed in greater detail inSurfaces, Interfaces, and Colloids: Principles and Applications, SecondEdition, Drew Meyers, 1999, John Wiley & Sons, Inc. and in ContactAngle, Wettability, and Adhesion, edited by Robert F. Gould (1964), bothof which are hereby incorporated by reference.

FIG. 2 is an exploded view of a fluidic system 120 formed in accordancewith one embodiment. The fluidic system 120 is configured to conveyliquid (not shown) between microplates 122 and 124 through a fluidicdevice 126. The microplate 122 may include an array 128 of source wells130 where each source well 130 contains an amount of the liquid. Thesource wells 130 include openings 131 for accessing the source wells130. The microplate 124 may include an array 132 of reaction wells 134that also have an opening 136. Each reaction well 134 may include asample region 140, such as a microarray on a chip, located at a bottom143 of the corresponding reaction well 134. The microplates 122 and 124may be, for example, multi-well plates. In another embodiment, themicroplate 124 may comprise a substrate and a gasket mounted to thesubstrate.

As shown, the microplate 122 is in an inverted position such that theopenings 131 of the source wells 130 face substantially in a directionwith a gravitational force direction F_(g) (i.e., a vertical directionalong an axis 190). The source wells 130 may be sized and shaped suchthat the liquid remains in the corresponding source wells 130 due tocapillary forces F_(c) when the microplate 122 is in the invertedposition. Capillary forces F_(c) include the adhesive and cohesiveforces experienced by the liquid within the source well 130. In suchpositions, the capillary forces F_(c) created by the liquid and thewalls of the source wells 130 are greater than the gravitational forceF_(g). The volume and composition of the liquid can be selected suchthat cohesive and adhesive forces are sufficient to retain the liquid inthe well.

The fluidic device 126 has a support structure 141 having an array 142of microfluidic tubes 144 coupled thereto. The fluidic device 126 isconfigured to be mounted to either or both of the microplates 122 and124. The support structure 141 may be substantially planar and extendalong a horizontal axis 192 when the fluidic device 126 is mounted toone of the microplates 122 and 124. Each tube 144 may have a commonorientation with respect to the other tubes 144. As shown, the tubes 144may extend substantially along the vertical axis 190 or substantiallyalong the direction of the gravitational force Fg. The arrays 128, 132,and 142 may be matching such that, when the fluidic device 126 ismounted to either of the microplates 122 and 124, the microfluidic tubes144 may be inserted into the corresponding wells.

By way of example, in order to convey liquid between the source wells130 and corresponding reaction wells 134, the fluidic device 126 may bemounted to the microplate 124. A portion of each tube 144 may beinserted through the opening 136 of a corresponding reaction well 134.The tube 144 may contact the bottom 143 of the reaction well 134 nearthe sample region 140 or may be suspended within a volume of thereaction well 134. The microplate 122 may then be lowered onto thefluidic device 126 such that a portion of each tube 144 is inserted intoa corresponding source well 130. When the portion of the tube 144advances through the opening 131 of the source well 130, the tube 144may displace a portion of a volume of the liquid therein forcing theliquid into the tube 144. Each tube 144 is configured to allow theliquid within the corresponding source well 130 to be drawn therethroughand into the corresponding reaction well 134. The tube 144 may beconfigured to locate a drop or a liquid aliquot onto the bottom 143 ofthe reaction well 134 and cover the sample region 140. Alternatively,the tube 144 may be shaped to locate the liquid onto a sidewall of thereaction well 134 or another desired location.

The fluidic device 126 may have mating features that engage or otherwisefasten the fluidic device 126 to a plate of source wells, a plate ofreaction wells or both. For example, a post (not shown) projecting fromthe fluidic device 126 may form an interference fit with a correspondingcavity (not shown) in the plate of source wells or the plate of reactionwells. Furthermore, other devices, such as tabs or a clamp, may be usedto hold the fluidic device 126 onto the plate of source wells or theplate of reaction wells. As such the mating features can providealignment of tubes to wells.

FIG. 3 is a perspective view of the fluidic device 126. The supportstructure 141 may have a generally planar or rectangular body 160 thatis configured to hold the array 142 of the tubes 144 in a commonorientation. The body 160 may include a pair of spaced apart beams 162and 164 that extend along a common plane and may be parallel to eachother. As shown, the beams 162 and 164 have a length L₁ and areseparated from each other by a distance D₁. The beams 162 and 164 may bejoined to each other by one or more bridge members 166 that extendacross the distance D₁ and provide support and stability to the fluidicdevice 126. Each tube 144 may be coupled to the support structure 141via a corresponding bridge member 166. As shown, the array 142 of thetubes 144 may be arranged in a plurality of rows and columns in agrid-like format. Alternatively, the tubes 144 may have otherarrangements. In some embodiments, the fluidic device 126 may beintegrally formed such that the support structure 141 and the tubes 144are made altogether through, e.g., an injection molding process.

Alternatively, the tubes 144 may be separately inserted into holeswithin the corresponding bridge member 166 or form a snap-fit with thebridge member 166. In another alternative embodiment, individual bridgemembers 166 may be integrally formed with a series of tubes 144. Eachbridge member 166 in such embodiments may be removably coupled (e.g.,through interference fitting) to a pair of beams to form the fluidicdevice 126. Thus, the array 142 of tubes 144 may be reconfigurable insome embodiments.

Each tube 144 may have an inlet 170, an outlet 172, and an open-sidedchannel 174 extending therebetween. The tube 144 may also have an inletportion 176 that is sized and shaped to be inserted into the source well130 (FIG. 2) and an outlet portion 178 that is sized and shaped to beinserted into the reaction well 134 (FIG. 2). The inlet and outletportions 176 and 178 may project a distance D₂ and D₃, respectively,from the corresponding bridge member 166. The distances D₂ and D₃ areconfigured along with other dimensions of the tubes 144, source wells130, and reaction wells 134 in order to facilitate conveying the liquidfrom the source well 130 to the reaction well 134.

FIG. 4 is a perspective view of the tube 144. The tube 144 is shown inrelation to axes 290, 292, and 294. The tube 144 includes a body 202that has the inlet 170, the outlet 172, and the open-sided channel 174extending therebetween along a central longitudinal axis 288 of thebody. The body 202 has a length L₂ that extends between the inlet 170and the outlet 172 along the longitudinal axis 288. As the body 202extends lengthwise along the longitudinal axis 288 a cross-sectionalshape of the body may vary. For example, the body 202 may have a widthW₁ that varies as the body 202 extends along the length L₂ of the body.Although the body 202 in FIG. 4 is substantially linear with respect tothe longitudinal axis 288, the body 202 is not required to be straight.For example, the body 202 may curve or shift in order to deposit theliquid at a desired location within the reaction well 134 (FIG. 2).

The body 202 of the tube 144 includes a pair of opposing arms 204 and206 that surround the longitudinal axis 288 and join each other at acenter portion 208 of the body 202. The body 202 has an inner surface212 and an exterior surface 214. The inner surface 212 defines thechannel 174. The channel 174 is open-sided such that when the liquidflows down the channel 174, the liquid is exposed to ambient orsurrounding air. As shown, a gap G extends along the length L₂ of thebody 202 separating the arms 204 and 206 from each other. Morespecifically, the arms 204 and 206 may have corresponding end portions214 and 215. When the gap G separates the arms 204 and 206, the endportions 214 and 215 of each arm 204 and 206, respectively, are spacedapart from each other by a gap distance D_(g). The gap G may extend theentire length L₂ from the inlet 170 to the outlet 172 as shown in FIG.4. However, in other embodiments, the gap G may extend along one or moreportions of the body 202 within intervening portions that do not have agap.

As shown in FIG. 4, the outlet 172 has a substantially planar front endwith respect to a plane that is formed by the axes 294 and 290 and thatis transverse to the longitudinal axis 288. However, in alternativeembodiments, the outlet 172 may be shaped as desired. For example, theoutlet 172 may be shaped to facilitate the tube 144 locating thereaction well 134 that the tube 144 is being inserted into. Morespecifically, the outlet 172 may form a point or a projection that has across-sectional area smaller than a cross-sectional area of the well.Likewise, the inlet 170 may be sized and shaped to facilitate locatingthe source well when the tube 144 is moved thereto.

Furthermore, the channel 174 has a cross-sectional area at the inlet 170and a cross-sectional area at the outlet 172. In a particularembodiment, the cross-sectional areas at the inlet 170 and at the outlet172 are different. For example, the cross-sectional area of the channel174 at the inlet 170 may be greater than the cross-sectional area of theoutlet 172.

FIG. 5 shows cross-sections C₁ and C₂ of the tube 144 taken transverseto the longitudinal axis 288 in FIG. 4. The cross-section C₁ is from theoutlet portion 178 (FIG. 3) and the cross-section C₂ is from the inletportion 176 (FIG. 3). The cross-sections C₁ and C₂ are described withreference to a plane P₃ that extends through the longitudinal axis 288and the center portion 208 and is perpendicular to a plane formed by theaxes 292 and 294. As shown, the plane P₃ may bisect the body 202 suchthat the arms 204 and 206 are symmetrical about the plane P₃.

The cross-sections C₁ and C₂ illustrate an interior contour 216 of thechannel 174 that is defined by the inner surface 212. The interiorcontour 216 includes the gap G (FIG. 4) that separates the opposing arms204 and 206 by a gap distance D_(g). The interior contour 216 may besized and shaped at different portions along the channel 174 tofacilitate controlling the flow of liquid (not shown). For example, theinner surface 212 may curve about the longitudinal axis 288 such thatthe interior contour 216 is substantially C-shaped or U-shaped. Thecross-section C₂ may be sized and shaped to be inserted into and receivethe liquid from the source well 130 and allow the liquid to be pulled bythe gravitational force F_(g) (FIG. 2) through the channel 174. Thecross-section C₁ may be sized and shaped to deposit the liquid onto adesired location within the reaction well 134 (FIG. 2).

By way of example, the channel 174 has maximum widths W₂ and W₃ atcross-sections C₁ and C₂, respectively, that extend between the arms 204and 206 along the axis 292. The cross-section C₁ also has a maximumheight H₁ that extends along the axis 294 from the center portion 208 toproximate the end portions 214 and 215. Likewise, the cross-section C₂has a maximum height H₂ that extends along the axis 294 from the centerportion 208 to a position proximate to the end portions 214 and 215. Theratio of the maximum height to the maximum width for a cross-section canbe any of a variety of ratios that support movement of a liquid. Inparticular embodiments, the ratio of maximum height to maximum width canbe at least 0.5 to 1, at least 1 to 1, at least 1.5 to 1 at least 5 to 1or the ratio can be higher. Alternatively or additionally, the ratio ofmaximum height to maximum width can be at most 10 to 1, at most 5 to 1,at most 1.5 to 1 or at most 1 to 1. Such ratios are particularly usefulfor tubes having a C-shaped or U-shaped cross-section, examples of whichare shown in FIGS. 5 and 6.

Accordingly, the cross-sections C_(I) and C₂ may have differentdimensions to control the flow of the liquid therethrough. As shown inFIG. 5, the width W₃ can be at least greater than the width W₂. The gapdistance D_(g) at the cross-section C₂ is greater than the gap distanceD_(g) at the cross-section C₁. The height H₂ is greater than the heightH₁. As such, a cross-sectional area of the channel 174 within the inletportion 176 is greater than a cross-sectional area of the channel 174 atthe outlet portion 178. Furthermore, the shapes of the interior contour216 at cross-section C₁ and at cross-section C₂ may also be different.As shown, the interior contour 216 may be substantially C-shaped at thecross-section C_(I), but may be substantially U-shaped at thecross-section C₂.

In some embodiments, the open-sided channel 174 may reduce the capillaryforces F_(c) (FIG. 2) that might impede or prevent the liquid fromflowing therethrough. Also, the dimensions of the inlet portion 176provide a larger cross-sectional area for the liquid to flowtherethrough as compared to the outlet portion 178. In such embodiments,the capillary forces F_(c) are reduced along the inlet portion 176 andthe flow of liquid may be faster therethrough than the flow of theliquid through the outlet portion 178.

However, the above description of the shapes and dimensions of theinterior contour 216 is only one example and the cross-sections ofinterior contour 216 may have different shapes and dimensions. Forexample, the cross-section C₁ may have dimensions that are slightlylarger than the dimensions of C₂.

The inner surface 212 may be hydrophobic or hydrophilic. Furthermore,the inner surface 212 of the interior contour 216 may have surfacecharacteristics that facilitate controlling the flow of the liquid fromthe source well 130 to the reaction well 134. In a particularembodiment, the inner surface 212 has a common surface energy throughoutthe channel 174. However, in other embodiments, the inner surface 212may have a surface energy gradient where one or more portions of theinner surface 212 are hydrophobic and one or more portions of the innersurface 212 are less hydrophobic. In other words, forces experienced bythe liquid at the liquid-solid interface may change as the liquid flowsdown the channel 174. Likewise, the surface energy gradient may beformed by hydrophilic surfaces.

FIGS. 6A-6C illustrate pairs of cross-sections taken from correspondingmicrofluidic tubes (not shown) formed in accordance with alternativeembodiments. More specifically, FIG. 6A shows cross-sections C₃ and C₄taken from an outlet portion and an inlet portion, respectively, of acorresponding microfluidic tube. The cross-section C₃ is similar to thecross-section C₁ (FIG. 5). However, the cross-section C₄ has an interiorcontour 316 with an inner surface 312 that completely surrounds thelongitudinal axis 318. For example, the interior contour 316 of thecross-section C₄ may be a circle, an oval, or another geometric shape.

FIG. 6B shows cross-sections C₅ and C₆ taken from an outlet portion andan inlet portion, respectively, of a corresponding microfluidic tube andshow an interior contour 326. As shown, the cross-section C₆ is similarto the cross-section C₂ (FIG. 5). However, the cross-section C₅ issubstantially open-faced. An inner surface 322 curves about alongitudinal axis 328, but does not surround or partially encircle thelongitudinal axis 328. FIG. 6C shows cross-sections C₇ and C₈ taken froman outlet portion and an inlet portion, respectively, of a correspondingmicrofluidic tube and show an interior contour 336. Unlike the previousdescribed cross-sections, the cross-section C₇ is not symmetrical abouta plane P₄ extending through a longitudinal axis 338. Suchcross-sections may be used when it is desired to deposit the liquid intoa certain location within the reaction well (e.g., in a corner of thewell or on a sidewall). Furthermore, an inner surface 332 of across-section is not required to curve about the correspondinglongitudinal axis. For example, as shown in FIG. 6C, the cross-sectionCg has a rectangular-shaped interior contour 336 that surrounds thelongitudinal axis 338.

In particular embodiments, the cross-sections C₁-C₈ described above withrespect to FIGS. 5 and 6A-6C may be along any portion of thecorresponding tube. Typically, at least a portion of the tube 144 willhave a cross-section with a discontinuity section, such as the gap G(FIG. 4). Furthermore, a microfluidic tube may have a uniformcross-section throughout the length of the tube. In another embodiment,the tube 144 (FIG. 5) has a circular cross-section throughout the lengthL₂ (FIG. 5) of the tube 144 (i.e., the tube 144 is not open-sided).

FIG. 7 illustrates the initial flow of a liquid L from the source well130 into the channel 174 of the tube 144. To convey the liquid L throughthe channel 174, the tube 144 (and support structure) may be held in adispensing orientation. In the dispensing orientation, the longitudinalaxis 288 of the tube 144 is held with respect to the gravitational forcedirection F_(g) such that the longitudinal axis 288 extends along thegravitational force direction F_(g). In the illustrated embodiment, thelongitudinal axis 288 and the gravitational force direction F_(g) aresubstantially parallel. However, the longitudinal axis 288 is notrequired to extend parallel to the gravitational force direction F_(g)when held in the dispensing orientation. For example, the longitudinalaxis 288 may form an angle with respect to the gravitational forcedirection F_(g) that allows gravity to draw or pull the liquid L throughthe channel 174. As an example, the longitudinal axis 288 may form anangle of 45 degrees or less with respect to the gravitational forcedirection F_(g) when in the dispensing orientation.

When the microplate 122 (FIG. 2) is inverted, the cohesive and adhesiveforces of the liquid L generate the capillary force F_(c) that isgreater than the gravitational force F_(g). As such, the liquid L isprevented from draining out of the source well 130. To remove the liquidL, the inlet 170 of the tube 144 is inserted through the opening 131 ofthe source well 130. When the inlet 170 is advanced into source well130, the liquid L is displaced by the inlet portion 176 of the tube 144.A portion of the liquid L may be forced into the channel 174 of the tube144. Furthermore, the inner surface 212 of the channel 174 may interactwith the liquid L through adhesive forces to facilitate drawing theliquid L from the source well 130. Upon contact of the liquid L by theinlet 170, cohesive forces holding the liquid L in the source well 130may be reduced such that liquid L is drawn into the inlet 170. Thegravitational force F_(g) may also facilitate drawing the liquid Ltherein. As the liquid L is drawn into the channel 174, the cohesiveforces of the liquid L may facilitate pulling the liquid L from thesource well 130 and into the channel 174. When a substantial portion ofthe liquid L is within the channel 174, the gravitational force F_(g)may continue to move the liquid L therethrough.

The dimensions of the tube 144 at the inlet portion 176 may be sized andshaped to control the flow of the liquid L therein. For example, thedimensions of the tube 144 may be configured based on the surface energyof the inner surface 212 and the surface tension of the liquid L. In oneembodiment, the inner surface 212 is hydrophobic and the liquid L is anaqueous or polar liquid. Alternatively, the inner surface 212 may behydrophilic and the liquid L may be non-polar. In other embodiments, atleast a portion of the inner surface 212 is hydrophobic and the liquid Lis a non-polar liquid or at least a portion of the inner surface 212 ishydrophilic and the liquid L is an aqueous or polar liquid.

Furthermore, the liquid L may be removed from the source well 130passively and/or conveyed passively through the tube 144. In analternative embodiment, the liquid L is actively removed from the sourcewell using a pump. The dimensions of the tube 144 may be reconfiguredbased upon the pumping abilities of the pump.

FIG. 8 is a side view of the tube 144 as the liquid L flows through thechannel 174 and into the reaction well 134 of the microplate 124 (FIG.2). In some embodiments, the outlet portion 178 of the tube 144 may beconfigured to reduce the flow of the liquid L as compared to the flow ofthe liquid L within the inlet portion 176 (FIG. 3). For example, thesize and shape of the outlet portion 178 and/or the surface energy ofthe inner surface 212 (FIG. 4) within the outlet portion 178 may beconfigured to reduce the flow of the liquid L as the liquid L approachesa predetermined point along the tube 144 (indicated as point A). Atpoint A, a sum of the forces experienced by the liquid L may result instopping the flow of the liquid L toward the bottom 143. For example, amagnitude of the capillary forces F_(c) may be greater than thegravitational force F_(g) experienced by the liquid L. As such, a volumeof the liquid L may gather within the channel 174 above point A. Thegravitational force F_(g) may cause the liquid L to flow out of the gapG. The liquid L may then flow into the reaction well 134. After apredetermined amount of time, a significant portion of the liquid L maybe loaded or deposited into the reaction well 134.

FIG. 8 illustrates an example of one embodiment that passively controlsthe flow of the liquid L into the reaction well 134 where significantforces experienced by the liquid L are the capillary forces F_(c) andthe gravitational force F_(g). However, in other embodiments, otherforces may be involved in controlling the flow of the liquid L. Forexample, the tubes 144 may experience a centripetal force that causesthe liquid L to flow downstream (i.e., from the inlet 170 toward theoutlet 172) until the liquid L reaches the point A where the capillaryforces F_(c) prevent further movement. Also, the liquid L may be pumped(i.e., by being pushed or vacuumed through the system) until the liquidL reaches point A. In alternative embodiments, the liquid L may be drawnthrough the tube 144 by capillary forces F_(c) and movement may bestopped by other forces (e.g., the gravitational force Fg, centripetalforce, forces through pumping or vacuuming).

Furthermore, in other embodiments, the liquid L may flow through thechannel 174 and out of the outlet 172. For example, the outlet portion178 may be sized and shaped such that the liquid L is capable of flowingtherethrough. Furthermore, the inner surface 212 (FIG. 4) of the tube144 may be coated with a substance or the tube may be manufactured froma predetermined material such that the surface energy of the innersurface 212 along the outlet portion 178 reduces the capillary forcesF_(c) to allow the liquid L to flow through the outlet 172.

When the liquid L is loaded into the reaction well 134, the liquid L maycover the sample region 140. in one embodiment, the sample region 140may comprise a chip having a chemical sample thereon. When the liquid Lis fully loaded onto the bottom 143 of the reaction well 134, a beadformed by the liquid L may entirely cover a surface of the sampleregion. The volume of the liquid L that is ultimately transferred intothe reaction well 134 can be controlled by selecting appropriatecharacteristics of the liquid L, such as a volume of the liquid L insource wells 130 before the transfer, and by selecting properties of thetube 144, such as volume capacity, tube shape, tube surfacecharacteristics and other characteristics set forth herein.Alternatively or additionally, the volume of transferred liquid L can becontrolled by the amount of time that the tubes 144 of the fluidicdevice 126 is in contact with the source wells 130 and/or reaction wells134.

FIG. 9 is an exploded view of a microplate 402 that may be used, forexample, with the fluidic system 120 described with reference to FIG. 2.The microplate 402 may be assembled from multiple components. in oneembodiment, the microplate 402 includes a gasket 404 that is mountedonto a substrate 406 having a mounting surface 408. The gasket 404 has abody 410 that is configured to be mounted to the mounting surface 408.For example, the body 410 may have opposing sides 412 and 414 and asubstantially uniform thickness T extending therebetween. The gasket 404may include an array 420 of passages 421 that extend through thethickness T. Each passage 421 is defined by a wall surface 430 (shown ina cut-out portion) that extends through the body 410 from an open inlet432 to an open outlet 434.

Also shown, the substrate 406 has a matching array 440 of sample regions422. The sample regions 422 include biomolecules that are immobilizedonto the mounting surface 408 of the substrate 406. The sample regions422 may be immobilized on chips that are positioned on the mountingsurface 408 or the sample regions 422 may be formed directly onto themounting surface 408. Also, the mounting surface 408 may besubstantially smooth and planar or, alternatively, may have cavities,recesses, indentations or the like.

To form the microplate 402, the gasket 404 is mounted onto the mountingsurface 408 of the substrate. The passages 421 of the gasket 404 arealigned with corresponding sample regions 422 so that the sample regions422 are exposed or are accessible through the corresponding passages421. The gasket 404 and substrate 406 may be held tightly together suchthat an interface 415 (shown in FIG. 11) extends along the mountingsurface 408 and the side 414. The interface 415 may be sealed so thatliquid does not leak therethrough. In some embodiments, an adhesive maybe placed on the side 414 and/or the mounting surface 408 in order tocouple the gasket 404 to the mounting surface 408. Also, the gasket 404and/or the substrate 406 may have mating features that engage each otherand fasten the gasket 404 and substrate 406 together. For example, apost (not shown) projecting from the substrate 406 may form aninterference fit with a corresponding cavity (not shown) in the gasket404. Furthermore, other devices, such as tabs or a clamp, may be used tohold the gasket 404 onto the mounting surface 408.

In alternative embodiments, the microplate 402 may have a unitary bodywhere the structural features of the gasket 404 and the substrate 406are integrally formed. For example, the microplate may be a multi-wellplate where one or more sample regions (e.g., a chip having a microarraythereon) are located in each well. In another alternative embodiment,the microplate or the gasket 404 may have the tubes 144 (FIG. 5)integrally formed with the microplate or the gasket 404. In suchembodiments, a fluidic device, such as the fluidic device 126 in FIG. 3,is not required.

FIG. 10 is a top plan view of a portion of the microplate 402. When thegasket 404 is mounted onto the mounting surface 408 of the substrate406, the passages 421 (FIG. 9) are closed off by the mounting surface408 thereby forming a well 442 having an open inlet 444, a closed end446, and a cavity 448 (FIG. 11) extending therebetween. The cavity 448is defined by a wall surface 450 that may form a plurality of sidewalls460-463. The wall surface 450 may also form a plurality of corners464-467 that join the sidewalls 460-463. As shown in FIG. 10, the wallsurface 450 has a cross-sectional contour 452 that may be sized andshaped for containing an approximate amount of the liquid L. Also shown,the well 442 has the sample region 422 located at the closed end 446.The sample region 422 may be centered within the well 442 or may bepositioned nearer to one of the sidewalls 460-463.

The cross-sectional contour 452 may be sized and shaped to facilitateremoving gases or microbubbles from a confined space that a liquid Lenters. More specifically, when the liquid L at least partially fillsthe well 442, the cross-sectional contour 452 is shaped to define aspacing 456 between the wall surface 450 and a liquid surface 458. Thespacing 456 may extend along one or more of the corners 464-467 and isconfigured to provide a gas exhaust path EP (shown in FIG. 11) to permitdischarge of gas from a well 442 that a liquid L enters.

The cross-sectional contour 452 may be rectangular-shaped and have alength L₃ and a width W₄. In some embodiments, the cross-sectionalcontour 452 has at least one dimension that is smaller than a dimensionthat the drop of liquid L would have been but for the cross-sectionalcontour 452 of the wall surface 450. For example, in accordance withsome embodiments, the cross-sectional contour 452 has a dimension (e.g.,the length L₃ or the width W₄) that is less than the resting diameterD_(R) (FIG. 1) of the amount of liquid L deposited into the well 442. Inother words, the cross-sectional contour 452 has a dimension that isless than a diameter of the amount of liquid L when it is deposited ontoa flat surface and is not contained by walls. Nevertheless, as set forthherein, an exhaust path EP (FIG. 11) can be present while the liquid Loccupies the well 442 defined by the cross-sectional contour 452. In aparticular embodiment, the cross-sectional contour 452 is substantiallyrectangular or square-shaped and the length L₃ and the width W₄ are bothless than the resting diameter D_(R) of the amount of liquid L depositedinto the well. Furthermore, in some embodiments, an area of a circlehaving the resting diameter D_(R) for the amount of liquid L depositedinto the well 452 is greater than an area of the cross-sectional contour452.

Also, the cross-sectional contour 452 may be sized and shaped to includeat least one continuous section, such as continuous sections 501-504,and at least one discontinuity section, such as discontinuity sections505-508, when the liquid L has at least partially filled the well 442.As used herein, a “continuous section” includes that section of thecross-sectional contour that contacts the liquid L when a thresholdamount of the liquid L has been deposited within the well 442. A“discontinuity section,” as used herein, includes that section of thecross-sectional contour that does not contact the liquid L when athreshold amount has been deposited within the well 442. A thresholdamount of the liquid L is an amount of the liquid L where the restingdiameter D_(R) of that amount of liquid L is greater than a dimension ofthe cross-sectional contour of the well.

The discontinuity sections 505-508 are shaped to provide thecorresponding spacing 456 between the surface 458 of the liquid L andthe wall surface 450 that extends from the closed end 446 of the well442 toward the open inlet 444. In some embodiments, the cross-sectionalcontour 452 defines a non-circular contour. The discontinuity sectionsof the wall surface 450 include corresponding corners 464-467.

FIG. 11 is a cross-sectional view of the well 442 taken along the line12-12 in FIG. 10. As shown, the gas exhaust paths EP₁ and EP₂ aredefined by the sidewalls 460, 462, and 463 (FIG. 10) and the liquidsurface 458. For example, the gas exhaust path EP₁ is defined by thesidewalls 460 and 463 and the liquid surface 458 and a surface of theclosed end 446. Both gas exhaust paths EP₁ and EP₂ extend from thesurface of the closed end 446 toward the open inlet 444. As shown, theclosed end 446 has a substantially planar surface. However, in otherembodiments, the closed end 446 may have a slightly curved surface ormay have a slight depression.

As shown in FIG. 11, the well 442 has a height H₃ and the liquid L has aheight H₄. When the liquid L is loaded into the well 442, the liquid Lmay fill a majority of a volume of the well 442 such that the continuoussection 504 of the cross-sectional contour 452 is in contact with theliquid L. For example, the height H₄ reached by the liquid L within thewell 442 may be substantially equal to the height H₃ while the well 442maintains the gas exhaust paths EP₁ and EP₂ therein. Also, although thegas exhaust paths EP₁ and EP₂ extend from the surface of the closed end446, alternative embodiments may include gas exhaust paths that extendalong less than the height H₃ or H₄. More specifically, the liquid L maycover the surface of the closed end 446 up to where the corners 464-467(FIG. 10) meet the closed end 446. In such embodiments, the gas exhaustpaths may extend along a majority of the height H₄ of the liquid Lwithin the well 442. For example, when the height H₄ is substantiallyequal to the height H₃, the gas exhaust paths may extend at least ¾ ofthe height H₃.

In order to determine the locations of the continuous sections 501-504(FIG. 10) and discontinuity sections 505-508 (FIG. 10), the dimensionsand shape of the cross-sectional contour 452 may be configured basedupon a surface energy of the wall surface 450 and the surface tension ofthe liquid L. In one example, the wall surface 450 may be hydrophobicand the liquid L may be aqueous or polar. Alternatively, the wallsurface 450 may be hydrophilic and the liquid L may be non-polar.

Furthermore, the composition of the surrounding gases (e.g., ambientair) and a range in temperatures experienced by the liquid L during thebiological or chemical assay may also be considered. As such, thecross-sectional contour 452 may be shaped to maintain the gas exhaustpath EP through a range of temperatures. For example, the gas exhaustpath EP may exist within the well 442 at an ambient temperature (e.g.,70° F.) when the liquid L is first loaded and also exist during athermal cycle where the temperature is changed, such as between 0° F.and 400° F. In particular applications, the temperature can be between75° F. and 150° F. For example, the methods and devices described hereincan be used for hybridization processes carried at temperatures belowabout 90° F. or more preferably below about 75° F. The methods anddevices can be used at temperatures where nucleic acids are denatured,such as at temperatures greater than 100° F. In particular embodiments,the methods and devices can be used in a humidified environment toreduce evaporation of liquids or under inert gas atmosphere to reduceoxidation and other reactions that would otherwise occur in the presenceof air. Accordingly, the size or shape of the spacing 456 and gasexhaust path EP may be affected by the temperature change. For example,the liquid surface 458 may expand closer to the wall surface 450 whenthe temperature increases. However, the gas exhaust path EP may stillexist between the closed end 446 and the open inlet 444 during thetemperature change.

In one embodiment, an amount of the liquid L loaded into the well 442 issignificantly more than an amount of liquid L necessary to completelycover the sample region 422 or the closed end 446. For example, theamount of liquid L loaded into the well 442 may be based upon an amountof liquid L that will evaporate after experiencing a thermal cycle.

FIGS. 12A-12E illustrate cross-sectional contours of wells (not shown)formed in accordance with alternative embodiments. The cross-sectionalcontours of the wells may have various shapes that deviate from thenatural shape of the liquid L when it is deposited onto a planarsurface. As shown in 12A, a cross-sectional contour 600 may include atleast one discontinuity section 602 formed by a rounded corner 604 inthe wall surface 606. A gas exhaust path EP₃ may be defined between therounded corner 604 and a surface of the liquid L. Furthermore, thecross-sectional contour may have a polygonal shape, such as a hexagonshown in FIG. 12B. Also, the cross-sectional contour may also be shapedas a triangle, a parallelogram (e.g., diamond-shaped), and a pentagon.

FIG. 12C illustrates a cross-sectional contour 610 having an elongatedoval shape. The cross-sectional contour 610 may include continuoussections 612 along shorter dimensions of the cross-sectional contour610, but may include discontinuity sections 614 along the longerdimensions. FIG. 12F illustrates a cross-sectional contour 630 having asemi-circle shape. The discontinuity sections may be formed at corners632 and 634.

FIGS. 12D and 12E include pocket projections 622 and 624, respectively.In FIG. 12D, a cross-sectional contour 620 has a substantiallysquare-like shape. However, the pocket projections 622 project outwardfrom where corners should be located. In FIG. 12E, a cross-sectionalcontour 623 has a substantially circular shape. However, the pocketprojections 624 project outward therefrom. As shown, continuous sectionsof the cross-sectional contour 623 have a first radius of curvature anddiscontinuity sections formed by the pocket projections 624 have asecond radius of curvature that is less than the first radius ofcurvature. Accordingly, embodiments described herein include wellshaving cross-sectional contours configured to facilitate venting gasesfrom the well into which the liquid is deposited. The shapes of thecross-sectional contours may be configured to conserve space or allowthe wells to be positioned closely to one another.

FIG. 13 is a block diagram illustrating a method 700 for performing amultiplex assay. The method 700 may use the fluidic devices and systemsdescribed above. First, a microplate may be provided that includesreaction wells having cross-sectional contours as described above forventing gases from a confined space that the liquid enters. The reactionwells may include sample regions therein. For example, the microplatemay be a pre-manufactured multi-well plate at 702. Alternatively, asubstrate may be provided at 704 having an array of sample regionsthereon. A gasket may then be mounted to the substrate at 706 so thatthe reaction wells having the cross-sectional contours are formed. Afluidic device having an array of tubes with open-sided channels isprovided at 708 and mounted to the microplate at 710 such that portionsof the tubes are located within corresponding reaction wells.

At 712, a microplate having an array of donor wells may be provided andinverted at 714. The donor wells include a liquid or a solution oftarget molecules that have a binding affinity for certain probes onmicroarrays of the sample regions. The target molecules may be labeledso that the target molecules are optically detectable (e.g., throughfluorescence). The tubes of the fluidic device may be inserted intocorresponding donor wells at 716 such that the tubes are held in adispensing orientation. As each tube is inserted into the donor well,the tube displaces the liquid within the donor well thereby forcing theliquid into the open-sided channel of the tube. The adhesive andcohesive forces and the gravitational force draw the liquid from thedonor well.

The liquid flows through the open-sided channel of the tube and isconveyed at 718 from the donor well and deposited or loaded into thecorresponding reaction well at 720. As the liquid enters each reactionwell and flows toward the sample region, the liquid at least partiallyfills the reaction well. The liquid may flow along a continuous sectionof the wall surface and remain separated from a discontinuity section ofthe wall surface. The separation forms a spacing and maintains a gasexhaust path to permit discharge of gas (i.e., vent) from the closed endof the well at 722.

The microplate may be inserted into a thermal cycler (e.g., oven) at 724where the microplate is heated to a desired temperature for apredetermined period of time. When the microplate is removed from thethermal cycler, the gasket may be removed at 726 from the substrate. Thesubstrate may then be washed at 728 to remove any undesired residue. Thesample regions may then be scanned by a detector at 730 to detect anyoptically detectable characteristics of the microarray. For example, thesubstrate may be scanned to detect a fluorescence level of the probes onthe microarray.

Alternatively, after the residue has been washed from the substrate at728, the substrate may be mounted by another gasket so that other fluidsmay be added to the substrate and processed through another thermalcycle for reacting with the probes of the sample regions.

Although the above described embodiments illustrate the gravitationalforce F_(g) being significant in controlling the flow of the liquid Lthrough the tube 144 and also while the liquid L rests within the well442, other forces may be applied to the fluidic system that areultimately stronger than the gravitational force F_(g) or work inconjunction with the gravitational force F_(g). For example, the liquidL may experience pumping or centripetal force through the tube 144 orwhile within the well 442. Furthermore, the surrounding environment(e.g., temperature, composition of the ambient air, pressure of theambient air) may be changed to affect the liquid L in a desired orpredetermined manner.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. While the specific components andprocesses described herein are intended to define the parameters of thevarious embodiments of the invention, they are by no means limiting andare exemplary embodiments. Many other embodiments will be apparent tothose of skill in the art upon reviewing the above description. Thescope of the invention should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format and are notintended to be interpreted based on 35 U.S.C. §112, sixth paragraph,unless and until such claim limitations expressly use the phrase “meansfor” followed by a statement of function void of further structure.

What is claimed is:
 1. A fluidic device for conveying liquid to a wellof a microplate, the device comprising: a support structure configuredto be mounted along the microplate; and a microfluidic tube coupled tothe support structure, the tube having an inlet, an outlet, and anopen-sided channel that extends longitudinally therebetween, the tubehaving a cross-section that includes an interior contour with a gaptherein, the gap extending at least partially along a length of thetube, the tube being configured to convey liquid to the well of themicroplate when the tube is held in a dispensing orientation.
 2. Thefluidic device in accordance with claim 1, wherein the gap in thecross-section is the only gap in the cross-section such that the gap islocated between two end portions of the tube in the cross-section, thetube extending continuously between the two end portions in thecross-section.
 3. The fluidic device in accordance with claim 1, whereinthe channel has a first cross-sectional area proximate to the inlet anda second cross-sectional area proximate to the outlet, the firstcross-sectional area being greater than the second cross-sectional area.4. The fluidic device in accordance with claim 1, wherein the tube isformed with opposing arms separated at the gap by a gap distance, thechannel having different first and second gap distances at the inlet andoutlet, respectively.
 5. The fluidic device in accordance with claim 1,wherein the gap extends along an entirety of the length of the tube. 6.The fluidic device in accordance with claim 1, wherein the channelextends between the inlet and the outlet along a central longitudinalaxis.
 7. A method of conveying liquid from a source well of amicroplate, the method comprising: inserting a microfluidic tube intothe source well of the microplate, the tube having an inlet, an outlet,and an open-sided channel that extends longitudinally therebetween, thetube having a cross-section that includes an interior contour with a gaptherein, the gap extending at least partially along a length of thetube; orienting the tube with respect to a gravitational force directioninto a dispensing orientation; and loading the liquid from the sourcewell into the tube, the liquid being exposed along the open-sidedchannel as the liquid flows down the tube.
 8. The method in accordancewith claim 7, wherein the loading operation includes flowing the liquidthrough the inlet of the tube.
 9. The method in accordance with claim 7,wherein the gap in the cross-section is the only gap in thecross-section such that the gap is located between two end portions ofthe tube in the cross-section, the tube extending continuously betweenthe two end portions in the cross-section.
 10. The method in accordancewith claim 7, wherein the channel has a first cross-sectional areaproximate to the inlet and a second cross-sectional area proximate tothe outlet, the first cross-sectional area being greater than the secondcross-sectional area.
 11. The method in accordance with claim 7, whereinthe tube is formed with opposing arms separated at the gap by a gapdistance, the channel having different first and second gap distances atthe inlet and outlet,
 12. The method in accordance with claim 7, whereinthe gap extends along an entirety of the length of the tube.
 13. Themethod in accordance with claim 7, wherein the channel extends betweenthe inlet and the outlet along a central longitudinal axis.
 14. Themethod in accordance with claim 7, wherein the dispensing orientationincludes the tube extending substantially parallel to the gravitationalforce direction.
 15. The method in accordance with claim 7, whereinloading the liquid into the tube includes passively conveying the liquidalong the channel.
 16. A microplate configured to facilitate venting awell that receives a liquid, the microplate comprising: a well having acavity with an open inlet and a closed end, the cavity extending betweenthe open inlet and the closed end, the cavity being defined by a wallsurface that has a cross-sectional contour that includes at least onecontinuous section and at least one discontinuity section, wherein theliquid partially fills the well when deposited therein, thecross-sectional contour being shaped to define a spacing between thediscontinuity section and the liquid, the spacing providing a gasexhaust path to permit discharge of gas from the closed end.
 17. Themicroplate in accordance with claim 16, wherein the spacing is definedby the closed end, the discontinuity section, and the liquid such thatthe spacing extends from a surface of the closed end toward the openinlet.
 18. The microplate in accordance with claim 16, wherein the wallsurface of the well is hydrophobic and wherein the well comprises aliquid that is polar or aqueous.
 19. The microplate in accordance withclaim 16, wherein the wall surface of the well is hydrophilic andwherein the well comprises a liquid that is non-polar.
 20. Themicroplate in accordance with claim 16, wherein the well comprises aliquid, the wall surface having a surface energy and the liquid having asurface tension, the cross-sectional contour of the cavity being shapedbased on the surface energy and the surface tension to provide thespacing between the liquid and the discontinuity section of the wallsurface.
 21. The microplate in accordance with claim 16, furthercomprising a gasket that has a passage and a substrate that has amounting surface, the passage of the gasket being defined by the wallsurface, wherein the gasket is mounted onto the mounting surface, thewell being formed by the mounting surface of the substrate and thepassage.
 22. The microplate in accordance with claim 21, wherein thecross-sectional contour of the wall surface is a non-circular contour.